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Re: [v6ops] IPv6-Only Preferred DHCPv4 option

Michael Richardson <mcr+ietf@sandelman.ca> Thu, 05 December 2019 13:53 UTC

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From: Michael Richardson <mcr+ietf@sandelman.ca>
To: Jen Linkova <furry13@gmail.com>
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Date: Thu, 05 Dec 2019 08:53:43 -0500
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Subject: Re: [v6ops] IPv6-Only Preferred DHCPv4 option
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Jen Linkova <furry13@gmail.com> wrote:
    > On Thu, Dec 5, 2019 at 5:22 AM Michael Richardson <mcr+ietf@sandelman.ca> wrote:
    >> A question that we had was whether or not hosts in a IPv6-mostly network
    >> should configure IPv4-LL addresses in order to speak to legacy-v4-only hosts.

    > Actually the more I think about it the more I believe the host should
    > be doing whatever they are doing w/o DHCPv4 presence.
    > Android does not configure IPv4 link-locals, MacOS does. Making the
    > same OS behaving differently ("no DHCPv4 whatsoever" vs "DHCPv4 server
    > responded with IPv6-only Preferred option") might be undesirable. As
    > an operator I'd expect that IPv6-only capable host would behave the
    > same way on a dedicated IPv6-only segment and on IPv6-mostly segment.

I see the logic: that they shouldn't change.
I think that a lot of desktop OSes go for IPv4-LL when DHCPv4 fails because
their IPv4 logic was written before IPv6 was a thing.

I think that if I set up an IPv6-mostly segment it is because I know that
there are hosts which speak IPv4 only, or which have IPv4-only applications
which do not work through NAT64.  (An IPv4-only printer is such an "application")

I think that the DHCPv4 option is a clue that configuring IPv4-LL addresses
is a good thing.   Does Android configure IPv4-LL when it has IPv4?  I think
that this also varies by the host OS.

Having said this, I don't feel strongly about it either way.

--
Michael Richardson <mcr+IETF@sandelman.ca>, Sandelman Software Works
 -= IPv6 IoT consulting =-

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